The type and extent of travel for professional footballers undertaking national team duties for a national football federation

Elite football (soccer) involves club, continental and international fixtures, requiring players to undertake extensive travel [1]. For a national football federation, this includes the transport of players between club and camp/tournament commitments, which is often a point of contention between respective organisations [2]. Partly this contention results from the effects of travel, whereby jet lag and travel fatigue can negatively affect physical performance [3–5] and athlete wellbeing [6, 7]. Given the scarcity of data on elite players following travel, an initial step for any national football federation is to understand the volume and nature of travel undertaken by national team players. Such insight may better identify the schedule, timelines and needs of athletes’ post travel. Better awareness of these travel needs can help maximise availability for training and minimise the impact of travel related stresses on performance or wellbeing. However, the regularity and volume of travel to national football team commitments has not previously been described. Further, travel demands are likely to vary significantly based on the location of the athlete and the national team camp. For countries outside of Europe, such as Australia, the travel demands and ensuing effects on player preparation can be substantial for both arrival into national team and on return to clubs [7]. Hence, detailed information regarding the type, frequency, and extent of travel for national team duties is important to aid in planning optimal travel schedules and interventions to assist players for international or club duty.


INTRODUCTION
In the absence of player data in the research literature, specific detail related to national team travel demands is needed, as the influence of jet lag and travel fatigue will differ based on a number of different factors related to the journey. Time zone shifts of > 3 h are likely to induce symptoms of jet lag, though athletic performance reductions exist with greater time zone differences [8,9]. For example, reductions in intermittent and maximal sprint performance [4] and jump performance [3,4] are observed after time zone shifts of > 8 h.
Similarly, long-haul travel of > 22 h can reduce sleep duration [5,6,10,11], which may explain elevated fatigue, [6,10] and reduced intermittent sprint performance [6] and lower body power [5] following arrival. In contrast, northbound travel of 10 h where athletes did not travel overnight had negligible effects on sleep and wellness [12]. The lack of effect from this flight may be attributed to the northward direction of travel and thus lack of significant time zone change, while it is also possible that the timing of the flight relative to the sleep period may be more critical than the duration of travel.
Thus, flights of roughly > 10 h with time zone changes of > 3 h should be of concern given the likelihood of inducing jet lag symptoms or The type and extent of travel for professional footballers undertaking national team duties for a national football federation AUTHORS: Ewan Clements 1,2 , Fabian Ehrmann 2 , Andrew Clark 2 , Mark Jones 2 , Donna Lu 1,2 , Rob Duffield 1,2 reported in 3 h groupings to better report the range and frequency of travel demands. For comparisons between club locations, all flights were labelled as being either outbound (travelling to national team duty, n = 244) or return (returning to club from national team, n = 244). Transition trips between national team commitments or to a location other than the players club were excluded from location-based comparisons (n = 71).

Statistical Analysis
Descriptive data for mean, standard deviation, median, minimum, and maximum values for all flight variables are reported. Shapiro-Wilk normality tests demonstrated that the data was not normally distributed, and comparisons between club location groups for all travel variables were assessed using non-parametric Kruskal-Wallis tests from the "stats" package in R [14]with significance set at p < 0.05.
Where a significant difference was observed between the groups, pairwise comparisons were made using Dunn Tests [15] with Holm corrected p values. All statistical tests were performed in the R statistical software [14].

RESULTS
A majority of trips involved time zone differences of ≤ 3 h (66%), though 34% of flights involved differences of > 3 h and 17% of flights involved large time differences of ≥ 8 h (Figure 1) Australian-based players had significantly greater return travel of this study is to describe the nature and extent of travel performed by Australian national team football players for international duties over a two-year period. In addition, this study compared the travel demands for national duties between players based in Australian (domestic), Asian and European club locations.

Participants
Participants were 58 male senior Australian national football (soccer) team representatives who had undertaken travel to train or compete for the national team between March 2018 and November 2019.

Through contractual agreements, participants provided consent to
Football Australia for the use of their anonymous data for research purposes, and human ethics approval was provided by the institutional Human Ethics Committee (ETH20 -5080).       This study shows a number of trips resulting in time zone differences of > 3 h (34%), which have been previously observed to induce jet lag symptoms in athletes [13, [16][17][18], though symptoms are expected to be more detrimental with greater time zone differences [19][20][21]. Although no performance measures were recorded in this study, 17% of trips, exceeded 8 h of time zone difference, with such time zone changes previously being shown to cause reductions in intermittent and maximal sprint as well as jump performance [3,4]. This study highlights that many national team trips for this federation have the potential to induce detrimental jet lag symptoms and thus practitioners should consider interventions that can hasten the rate at which an athlete adapts to time zone changes. Further, 36% of trips required overnight air travel, with this potentially putting athletes at risk of impaired sleep [6,10,11]. Impairments in sleep may then have further implications for wellbeing and performance [5,6,10,22], highlighting the need for appropriate strategies to monitor and promote sleep during travel [10,11,13].

Data Collection
Related to the overnight nature of travel, 33% of flights arrived in the first half of the day (24:00-12:00), and thus are likely to involve longer durations between full sleep periods which may have additional consequences for sleep and adaptation [23]. For such trips, daytime naps may be useful where athletes were unable to obtain sufficient sleep during travel [24]. Currently, no studies have report-  a concern for Australian-based players, the greater concern may result from travel fatigue due to longer travel durations and potential implications of long-duration flights [9,19,21]. However, as longhaul daytime travel ≤ 10 h has not been observed to affect performance and wellbeing [12], similar travel fatigue symptoms theoretically may persist in all groups given overnight travel requirements were similar [5,6,10]. The similarities in overnight travel amongst all players suggests interventions to reduce travel induced sleep loss should be of focus for national team practitioners for player arrival into camp. Accordingly, a need for attention on circadian re-entrainment exists for European-based players, while sleep-promoting interventions during and after travel are required for all players arriving for national team duties.
Given the prevalence of fixture congestion in elite football [1], returning players to clubs from national teams requires effective communication between national and club team staff to enhance player recovery and selection availability. During return travel, Australianbased players had the worst travel schedules, with more eastward trips, longer travel durations and more trips requiring overnight travel. These travel schedules may place the athletes at greater likelihood of jet lag due to the longer lasting effects following eastward travel [4,26], while longer travel durations and overnight flights have previously been observed to reduce sleep and increase fatigue [5,11].
Therefore, additional focus on hastening time zone adaptations in players returning to Australian clubs is suggested, while attempts to reduce sleep deficits from overnight travel are also recommended.
Earlier arrivals have previously been observed to contribute to greater symptoms of jet lag due to longer durations between full sleep periods [23]; and should also be considered in Australian-based players who on average arrived significantly earlier than European-based players. While greater attention is required for Australian-based players, the average time zone differences of 3.5 ± 3.2 h may still be enough to induce jet lag in European-based players [8,9,19]. Given these players largely travelled westward on return to clubs, it is speculative whether these symptoms may potentially alleviate quicker than eastward travelling players [4,20,26].
Despite the novelty of these results, several limitations should be considered when interpreting these findings. Importantly, as this study did not obtain any measures of wellness, performance or sleep from players, any suggested effects of travel are based on previous research. Additionally, the travel demands represent a case study of one national team undertaking tournaments at that point of the time.
Furthermore, while a broad date range was used there is likely a bias in the findings based on the location of tournaments. Different travel demands are therefore likely to be observed between other national teams and time frames. Lastly, while a majority of international travel is performed via aircraft, this study does not consider additional modes of transport i.e. road or railway travel and its potential effects on players, nor does it account for travel to and from the airport [8].

CONCLUSIONS
Overall, this study provides a detailed case-study of the type and extent of travel involved in a national football team, while demonstrating that these demands are likely to differ based on a player's club location.
Travel for national team duties are diverse, and there remains many schedules that require planning to maximise performance and wellbeing. A single squad-wise approach to travel scheduling may not be appropriate as the nature of travel differs significantly between player's club locations. For the Australian national team, travel into camp is likely most demanding for European-based players, while Australianbased players may be more at risk of negative travel consequences following return travel. As such, it is important to consider the specific demands of players on an individual or at least regional basis.